I think in a piece by John Baez we learn that the physics of an expanding and collapsing dust filled universe is the same as the physics of a bouncing ball, Radius, R, verses time and height, h, verses time? If so are there counterparts to the kinetic and potential energy of a bouncing ball and an expanding and colapsing dust filled universe? It seems that when R and h are maximum we have max potential energy and when R and h are near zero we have max kinetic energy, if General Relativity has "things" like potential and kinetic energy? If you and I were nearby dust particles, in an expanding and collapsing universe, in the expansion stage say, we could estimate our potential and kinetic energies of each other by observation? I can "measure" your distance and velocity and thus estimate kinetic and potential energy? If When a gravitational wave goes by does space-time kind of "vibrate"? If so can we identify parts of the energy of a gravitational wave as being part "kinetic" and part "potential"? Could an oscillating dust filled universe be considered a "standing wave" because the potential and kinetic energy are 90 degrees out of phase? Thanks for any help!